A known tandem image forming apparatus is provided with photosensitive members, which are horizontally arranged in tandem with each other, in association with yellow, magenta, cyan and black toner. Such a tandem image forming apparatus can print in color at substantially the same speed as printing in monochrome, because a toner image of each color is formed substantially at the same time on the corresponding one of the photosensitive members and each of the different colored images is sequentially laid on top of each other on a sheet while the sheet passes through the photosensitive members.
Tandem-type color image forming apparatus can include a photosensitive member cartridge in which photosensitive members for each color are supported by a frame. The photosensitive member cartridge is slidingly attached to and removed from an apparatus body, and developing cartridges for developing an electrical latent image formed on each photosensitive member are attached to and removed from the frame.
In addition, guide ridges are formed on two opposing side surfaces of each developing cartridge. At the inner upper sides of two opposing side plates of the frame, there are provided guide grooves for receiving the guide ridges at constant positions corresponding to the photosensitive members. The guide ridges are inserted from above in the associated guide grooves, so that the developing cartridges are mounted in the frame. The developing cartridges are withdrawn from the frame along the guide grooves. The frame is provided with fixing levers in association with the guide grooves. The developing cartridges are fixed with respect to the associated photosensitive members by the fixing levers.